// Copyright (c) 2021, gottingen group.
// All rights reserved.
// Created by liyinbin lijippy@163.com
//
// -----------------------------------------------------------------------------
// File: flat_hash_map.h
// -----------------------------------------------------------------------------
//
// An `abel::flat_hash_map<K, V>` is an unordered associative container of
// unique keys and associated values designed to be a more efficient replacement
// for `std::unordered_map`. Like `unordered_map`, search, insertion, and
// deletion of map elements can be done as an `O(1)` operation. However,
// `flat_hash_map` (and other unordered associative containers known as the
// collection of abel "Swiss tables") contain other optimizations that result
// in both memory and computation advantages.
//
// In most cases, your default choice for a hash map should be a map of type
// `flat_hash_map`.

#ifndef ABEL_CONTAINER_FLAT_HASH_MAP_H_
#define ABEL_CONTAINER_FLAT_HASH_MAP_H_

#include <cstddef>
#include <new>
#include <type_traits>
#include <utility>

#include "abel/algorithm/container.h"
#include "abel/container/internal/container_memory.h"
#include "abel/container/internal/hash_function_defaults.h"  // IWYU pragma: export
#include "abel/container/internal/raw_hash_map.h"  // IWYU pragma: export
#include "abel/memory/memory.h"

namespace abel {

    namespace container_internal {
        template<class K, class V>
        struct flat_hash_map_policy;
    }  // namespace container_internal

    // -----------------------------------------------------------------------------
    // abel::flat_hash_map
    // -----------------------------------------------------------------------------
    //
    // An `abel::flat_hash_map<K, V>` is an unordered associative container which
    // has been optimized for both speed and memory footprint in most common use
    // cases. Its interface is similar to that of `std::unordered_map<K, V>` with
    // the following notable differences:
    //
    // * Requires keys that are CopyConstructible
    // * Requires values that are MoveConstructible
    // * Supports heterogeneous lookup, through `find()`, `operator[]()` and
    //   `insert()`, provided that the map is provided a compatible heterogeneous
    //   hashing function and equality operator.
    // * Invalidates any references and pointers to elements within the table after
    //   `rehash()`.
    // * Contains a `capacity()` member function indicating the number of element
    //   slots (open, deleted, and empty) within the hash map.
    // * Returns `void` from the `erase(iterator)` overload.
    //
    // By default, `flat_hash_map` uses the `abel::hash` hashing framework.
    // All fundamental and abel types that support the `abel::hash` framework have
    // a compatible equality operator for comparing insertions into `flat_hash_map`.
    // If your type is not yet supported by the `abel::hash` framework, see
    // abel/hash/hash.h for information on extending abel hashing to user-defined
    // types.
    //
    // NOTE: A `flat_hash_map` stores its value types directly inside its
    // implementation array to avoid memory indirection. Because a `flat_hash_map`
    // is designed to move data when rehashed, map values will not retain pointer
    // stability. If you require pointer stability, or if your values are large,
    // consider using `abel::flat_hash_map<Key, std::unique_ptr<Value>>` instead.
    // If your types are not moveable or you require pointer stability for keys,
    // consider `abel::node_hash_map`.
    //
    // Example:
    //
    //   // Create a flat hash map of three strings (that map to strings)
    //   abel::flat_hash_map<std::string, std::string> ducks =
    //     {{"a", "huey"}, {"b", "dewey"}, {"c", "louie"}};
    //
    //  // Insert a new element into the flat hash map
    //  ducks.insert({"d", "donald"});
    //
    //  // Force a rehash of the flat hash map
    //  ducks.rehash(0);
    //
    //  // Find the element with the key "b"
    //  std::string search_key = "b";
    //  auto result = ducks.find(search_key);
    //  if (result != ducks.end()) {
    //    std::cout << "Result: " << result->second << std::endl;
    //  }
    template<class K, class V,
            class Hash = abel::container_internal::hash_default_hash<K>,
            class Eq = abel::container_internal::hash_default_eq<K>,
            class Allocator = std::allocator<std::pair<const K, V>>>
    class flat_hash_map : public abel::container_internal::raw_hash_map<
            abel::container_internal::flat_hash_map_policy<K, V>,
            Hash, Eq, Allocator> {
        using Base = typename flat_hash_map::raw_hash_map;

    public:
        // Constructors and Assignment Operators
        //
        // A flat_hash_map supports the same overload set as `std::unordered_map`
        // for construction and assignment:
        //
        // *  Default constructor
        //
        //    // No allocation for the table's elements is made.
        //    abel::flat_hash_map<int, std::string> map1;
        //
        // * Initializer List constructor
        //
        //   abel::flat_hash_map<int, std::string> map2 =
        //       {{1, "huey"}, {2, "dewey"}, {3, "louie"},};
        //
        // * Copy constructor
        //
        //   abel::flat_hash_map<int, std::string> map3(map2);
        //
        // * Copy assignment operator
        //
        //  // Hash functor and Comparator are copied as well
        //  abel::flat_hash_map<int, std::string> map4;
        //  map4 = map3;
        //
        // * Move constructor
        //
        //   // Move is guaranteed efficient
        //   abel::flat_hash_map<int, std::string> map5(std::move(map4));
        //
        // * Move assignment operator
        //
        //   // May be efficient if allocators are compatible
        //   abel::flat_hash_map<int, std::string> map6;
        //   map6 = std::move(map5);
        //
        // * Range constructor
        //
        //   std::vector<std::pair<int, std::string>> v = {{1, "a"}, {2, "b"}};
        //   abel::flat_hash_map<int, std::string> map7(v.begin(), v.end());
        flat_hash_map() {}

        using Base::Base;

        // flat_hash_map::begin()
        //
        // Returns an iterator to the beginning of the `flat_hash_map`.
        using Base::begin;

        // flat_hash_map::cbegin()
        //
        // Returns a const iterator to the beginning of the `flat_hash_map`.
        using Base::cbegin;

        // flat_hash_map::cend()
        //
        // Returns a const iterator to the end of the `flat_hash_map`.
        using Base::cend;

        // flat_hash_map::end()
        //
        // Returns an iterator to the end of the `flat_hash_map`.
        using Base::end;

        // flat_hash_map::capacity()
        //
        // Returns the number of element slots (assigned, deleted, and empty)
        // available within the `flat_hash_map`.
        //
        // NOTE: this member function is particular to `abel::flat_hash_map` and is
        // not provided in the `std::unordered_map` API.
        using Base::capacity;

        // flat_hash_map::empty()
        //
        // Returns whether or not the `flat_hash_map` is empty.
        using Base::empty;

        // flat_hash_map::max_size()
        //
        // Returns the largest theoretical possible number of elements within a
        // `flat_hash_map` under current memory constraints. This value can be thought
        // of the largest value of `std::distance(begin(), end())` for a
        // `flat_hash_map<K, V>`.
        using Base::max_size;

        // flat_hash_map::size()
        //
        // Returns the number of elements currently within the `flat_hash_map`.
        using Base::size;

        // flat_hash_map::clear()
        //
        // Removes all elements from the `flat_hash_map`. Invalidates any references,
        // pointers, or iterators referring to contained elements.
        //
        // NOTE: this operation may shrink the underlying buffer. To avoid shrinking
        // the underlying buffer call `erase(begin(), end())`.
        using Base::clear;

        // flat_hash_map::erase()
        //
        // Erases elements within the `flat_hash_map`. Erasing does not trigger a
        // rehash. Overloads are listed below.
        //
        // void erase(const_iterator pos):
        //
        //   Erases the element at `position` of the `flat_hash_map`, returning
        //   `void`.
        //
        //   NOTE: returning `void` in this case is different than that of STL
        //   containers in general and `std::unordered_map` in particular (which
        //   return an iterator to the element following the erased element). If that
        //   iterator is needed, simply post increment the iterator:
        //
        //     map.erase(it++);
        //
        // iterator erase(const_iterator first, const_iterator last):
        //
        //   Erases the elements in the open interval [`first`, `last`), returning an
        //   iterator pointing to `last`.
        //
        // size_type erase(const key_type& key):
        //
        //   Erases the element with the matching key, if it exists.
        using Base::erase;

        // flat_hash_map::insert()
        //
        // Inserts an element of the specified value into the `flat_hash_map`,
        // returning an iterator pointing to the newly inserted element, provided that
        // an element with the given key does not already exist. If rehashing occurs
        // due to the insertion, all iterators are invalidated. Overloads are listed
        // below.
        //
        // std::pair<iterator,bool> insert(const init_type& value):
        //
        //   Inserts a value into the `flat_hash_map`. Returns a pair consisting of an
        //   iterator to the inserted element (or to the element that prevented the
        //   insertion) and a bool denoting whether the insertion took place.
        //
        // std::pair<iterator,bool> insert(T&& value):
        // std::pair<iterator,bool> insert(init_type&& value):
        //
        //   Inserts a moveable value into the `flat_hash_map`. Returns a pair
        //   consisting of an iterator to the inserted element (or to the element that
        //   prevented the insertion) and a bool denoting whether the insertion took
        //   place.
        //
        // iterator insert(const_iterator hint, const init_type& value):
        // iterator insert(const_iterator hint, T&& value):
        // iterator insert(const_iterator hint, init_type&& value);
        //
        //   Inserts a value, using the position of `hint` as a non-binding suggestion
        //   for where to begin the insertion search. Returns an iterator to the
        //   inserted element, or to the existing element that prevented the
        //   insertion.
        //
        // void insert(InputIterator first, InputIterator last):
        //
        //   Inserts a range of values [`first`, `last`).
        //
        //   NOTE: Although the STL does not specify which element may be inserted if
        //   multiple keys compare equivalently, for `flat_hash_map` we guarantee the
        //   first match is inserted.
        //
        // void insert(std::initializer_list<init_type> ilist):
        //
        //   Inserts the elements within the initializer list `ilist`.
        //
        //   NOTE: Although the STL does not specify which element may be inserted if
        //   multiple keys compare equivalently within the initializer list, for
        //   `flat_hash_map` we guarantee the first match is inserted.
        using Base::insert;

        // flat_hash_map::insert_or_assign()
        //
        // Inserts an element of the specified value into the `flat_hash_map` provided
        // that a value with the given key does not already exist, or replaces it with
        // the element value if a key for that value already exists, returning an
        // iterator pointing to the newly inserted element.  If rehashing occurs due
        // to the insertion, all existing iterators are invalidated. Overloads are
        // listed below.
        //
        // pair<iterator, bool> insert_or_assign(const init_type& k, T&& obj):
        // pair<iterator, bool> insert_or_assign(init_type&& k, T&& obj):
        //
        //   Inserts/Assigns (or moves) the element of the specified key into the
        //   `flat_hash_map`.
        //
        // iterator insert_or_assign(const_iterator hint,
        //                           const init_type& k, T&& obj):
        // iterator insert_or_assign(const_iterator hint, init_type&& k, T&& obj):
        //
        //   Inserts/Assigns (or moves) the element of the specified key into the
        //   `flat_hash_map` using the position of `hint` as a non-binding suggestion
        //   for where to begin the insertion search.
        using Base::insert_or_assign;

        // flat_hash_map::emplace()
        //
        // Inserts an element of the specified value by constructing it in-place
        // within the `flat_hash_map`, provided that no element with the given key
        // already exists.
        //
        // The element may be constructed even if there already is an element with the
        // key in the container, in which case the newly constructed element will be
        // destroyed immediately. Prefer `try_emplace()` unless your key is not
        // copyable or moveable.
        //
        // If rehashing occurs due to the insertion, all iterators are invalidated.
        using Base::emplace;

        // flat_hash_map::emplace_hint()
        //
        // Inserts an element of the specified value by constructing it in-place
        // within the `flat_hash_map`, using the position of `hint` as a non-binding
        // suggestion for where to begin the insertion search, and only inserts
        // provided that no element with the given key already exists.
        //
        // The element may be constructed even if there already is an element with the
        // key in the container, in which case the newly constructed element will be
        // destroyed immediately. Prefer `try_emplace()` unless your key is not
        // copyable or moveable.
        //
        // If rehashing occurs due to the insertion, all iterators are invalidated.
        using Base::emplace_hint;

        // flat_hash_map::try_emplace()
        //
        // Inserts an element of the specified value by constructing it in-place
        // within the `flat_hash_map`, provided that no element with the given key
        // already exists. Unlike `emplace()`, if an element with the given key
        // already exists, we guarantee that no element is constructed.
        //
        // If rehashing occurs due to the insertion, all iterators are invalidated.
        // Overloads are listed below.
        //
        //   pair<iterator, bool> try_emplace(const key_type& k, Args&&... args):
        //   pair<iterator, bool> try_emplace(key_type&& k, Args&&... args):
        //
        // Inserts (via copy or move) the element of the specified key into the
        // `flat_hash_map`.
        //
        //   iterator try_emplace(const_iterator hint,
        //                        const init_type& k, Args&&... args):
        //   iterator try_emplace(const_iterator hint, init_type&& k, Args&&... args):
        //
        // Inserts (via copy or move) the element of the specified key into the
        // `flat_hash_map` using the position of `hint` as a non-binding suggestion
        // for where to begin the insertion search.
        //
        // All `try_emplace()` overloads make the same guarantees regarding rvalue
        // arguments as `std::unordered_map::try_emplace()`, namely that these
        // functions will not move from rvalue arguments if insertions do not happen.
        using Base::try_emplace;

        // flat_hash_map::extract()
        //
        // Extracts the indicated element, erasing it in the process, and returns it
        // as a C++17-compatible node handle. Overloads are listed below.
        //
        // node_type extract(const_iterator position):
        //
        //   Extracts the key,value pair of the element at the indicated position and
        //   returns a node handle owning that extracted data.
        //
        // node_type extract(const key_type& x):
        //
        //   Extracts the key,value pair of the element with a key matching the passed
        //   key value and returns a node handle owning that extracted data. If the
        //   `flat_hash_map` does not contain an element with a matching key, this
        //   function returns an empty node handle.
        using Base::extract;

        // flat_hash_map::merge()
        //
        // Extracts elements from a given `source` flat hash map into this
        // `flat_hash_map`. If the destination `flat_hash_map` already contains an
        // element with an equivalent key, that element is not extracted.
        using Base::merge;

        // flat_hash_map::swap(flat_hash_map& other)
        //
        // Exchanges the contents of this `flat_hash_map` with those of the `other`
        // flat hash map, avoiding invocation of any move, copy, or swap operations on
        // individual elements.
        //
        // All iterators and references on the `flat_hash_map` remain valid, excepting
        // for the past-the-end iterator, which is invalidated.
        //
        // `swap()` requires that the flat hash map's hashing and key equivalence
        // functions be Swappable, and are exchanged using unqualified calls to
        // non-member `swap()`. If the map's allocator has
        // `std::allocator_traits<allocator_type>::propagate_on_container_swap::value`
        // set to `true`, the allocators are also exchanged using an unqualified call
        // to non-member `swap()`; otherwise, the allocators are not swapped.
        using Base::swap;

        // flat_hash_map::rehash(count)
        //
        // Rehashes the `flat_hash_map`, setting the number of slots to be at least
        // the passed value. If the new number of slots increases the load factor more
        // than the current maximum load factor
        // (`count` < `size()` / `max_load_factor()`), then the new number of slots
        // will be at least `size()` / `max_load_factor()`.
        //
        // To force a rehash, pass rehash(0).
        //
        // NOTE: unlike behavior in `std::unordered_map`, references are also
        // invalidated upon a `rehash()`.
        using Base::rehash;

        // flat_hash_map::reserve(count)
        //
        // Sets the number of slots in the `flat_hash_map` to the number needed to
        // accommodate at least `count` total elements without exceeding the current
        // maximum load factor, and may rehash the container if needed.
        using Base::reserve;

        // flat_hash_map::at()
        //
        // Returns a reference to the mapped value of the element with key equivalent
        // to the passed key.
        using Base::at;

        // flat_hash_map::contains()
        //
        // Determines whether an element with a key comparing equal to the given `key`
        // exists within the `flat_hash_map`, returning `true` if so or `false`
        // otherwise.
        using Base::contains;

        // flat_hash_map::count(const Key& key) const
        //
        // Returns the number of elements with a key comparing equal to the given
        // `key` within the `flat_hash_map`. note that this function will return
        // either `1` or `0` since duplicate keys are not allowed within a
        // `flat_hash_map`.
        using Base::count;

        // flat_hash_map::equal_range()
        //
        // Returns a closed range [first, last], defined by a `std::pair` of two
        // iterators, containing all elements with the passed key in the
        // `flat_hash_map`.
        using Base::equal_range;

        // flat_hash_map::find()
        //
        // Finds an element with the passed `key` within the `flat_hash_map`.
        using Base::find;

        // flat_hash_map::operator[]()
        //
        // Returns a reference to the value mapped to the passed key within the
        // `flat_hash_map`, performing an `insert()` if the key does not already
        // exist.
        //
        // If an insertion occurs and results in a rehashing of the container, all
        // iterators are invalidated. Otherwise iterators are not affected and
        // references are not invalidated. Overloads are listed below.
        //
        // T& operator[](const Key& key):
        //
        //   Inserts an init_type object constructed in-place if the element with the
        //   given key does not exist.
        //
        // T& operator[](Key&& key):
        //
        //   Inserts an init_type object constructed in-place provided that an element
        //   with the given key does not exist.
        using Base::operator[];

        // flat_hash_map::bucket_count()
        //
        // Returns the number of "buckets" within the `flat_hash_map`. Note that
        // because a flat hash map contains all elements within its internal storage,
        // this value simply equals the current capacity of the `flat_hash_map`.
        using Base::bucket_count;

        // flat_hash_map::load_factor()
        //
        // Returns the current load factor of the `flat_hash_map` (the average number
        // of slots occupied with a value within the hash map).
        using Base::load_factor;

        // flat_hash_map::max_load_factor()
        //
        // Manages the maximum load factor of the `flat_hash_map`. Overloads are
        // listed below.
        //
        // float flat_hash_map::max_load_factor()
        //
        //   Returns the current maximum load factor of the `flat_hash_map`.
        //
        // void flat_hash_map::max_load_factor(float ml)
        //
        //   Sets the maximum load factor of the `flat_hash_map` to the passed value.
        //
        //   NOTE: This overload is provided only for API compatibility with the STL;
        //   `flat_hash_map` will ignore any set load factor and manage its rehashing
        //   internally as an implementation detail.
        using Base::max_load_factor;

        // flat_hash_map::get_allocator()
        //
        // Returns the allocator function associated with this `flat_hash_map`.
        using Base::get_allocator;

        // flat_hash_map::hash_function()
        //
        // Returns the hashing function used to hash the keys within this
        // `flat_hash_map`.
        using Base::hash_function;

        // flat_hash_map::key_eq()
        //
        // Returns the function used for comparing keys equality.
        using Base::key_eq;
    };

    // erase_if(flat_hash_map<>, Pred)
    //
    // Erases all elements that satisfy the predicate `pred` from the container `c`.
    template<typename K, typename V, typename H, typename E, typename A,
            typename Predicate>
    void erase_if(flat_hash_map<K, V, H, E, A> &c, Predicate pred) {
        container_internal::erase_if(pred, &c);
    }

    template<typename T>
    using ignore_case_flat_hash_map = flat_hash_map<std::string, T, abel::container_internal::case_string_hash,
            abel::container_internal::case_string_equal>;

    namespace container_internal {

        template<class K, class V>
        struct flat_hash_map_policy {
            using slot_policy = container_internal::map_slot_policy<K, V>;
            using slot_type = typename slot_policy::slot_type;
            using key_type = K;
            using mapped_type = V;
            using init_type = std::pair</*non const*/ key_type, mapped_type>;

            template<class Allocator, class... Args>
            static void construct(Allocator *alloc, slot_type *slot, Args &&... args) {
                slot_policy::construct(alloc, slot, std::forward<Args>(args)...);
            }

            template<class Allocator>
            static void destroy(Allocator *alloc, slot_type *slot) {
                slot_policy::destroy(alloc, slot);
            }

            template<class Allocator>
            static void transfer(Allocator *alloc, slot_type *new_slot,
                                 slot_type *old_slot) {
                slot_policy::transfer(alloc, new_slot, old_slot);
            }

            template<class F, class... Args>
            static decltype(abel::container_internal::DecomposePair(
                    std::declval<F>(), std::declval<Args>()...))
            apply(F &&f, Args &&... args) {
                return abel::container_internal::DecomposePair(std::forward<F>(f),
                                                               std::forward<Args>(args)...);
            }

            static size_t space_used(const slot_type *) { return 0; }

            static std::pair<const K, V> &element(slot_type *slot) { return slot->value; }

            static V &value(std::pair<const K, V> *kv) { return kv->second; }

            static const V &value(const std::pair<const K, V> *kv) { return kv->second; }
        };

    }  // namespace container_internal

    namespace container_algorithm_internal {

        // Specialization of trait in abel/algorithm/container.h
        template<class Key, class T, class Hash, class KeyEqual, class Allocator>
        struct is_unordered_container<
                abel::flat_hash_map<Key, T, Hash, KeyEqual, Allocator>> : std::true_type {
        };

    }  // namespace container_algorithm_internal


}  // namespace abel

#endif  // ABEL_CONTAINER_FLAT_HASH_MAP_H_
